The situation to the north worsened after an Israeli airstrike killed a senior Hezbollah military commander in southern Lebanon. Hezbollah retaliated by firing hundreds of rockets and explosive drones into northern Israel.

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Israeli officials have threatened a military offensive in Lebanon if there is no negotiated end to push Hezbollah away from the border.

In a recent speech, Hezbollah leader Hassan Nasrallah said that militant leaders from Iran, Iraq, Syria, Yemen and other countries have previously offered to send tens of thousands of fighters to help Hezbollah, but he said the group already has more than 100,000 fighters.

He said, "We told them, thank you, but we are overwhelmed by the numbers we have.” He added the battle in its current form is using only a portion of Hezbollah's manpower, an apparent reference to the specialized fighters who fire missiles and drones.

But that could change in the event of an all-out war. Nasrallah hinted at that possibility in a speech in 2017 in which he said fighters from Iran, Iraq, Yemen, Afghanistan and Pakistan "will be partners" of such a war.

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Officials from Lebanese and Iraqi groups backed by Iran say Iran-backed fighters from around the region will join in if war erupts on the Lebanon-Israel border. Thousands of such fighters are already deployed in Syria and could easily slip through the porous and unmarked border.

"We will be (fighting) shoulder to shoulder with Hezbollah" if an all-out war breaks out, one official with an Iran-backed group in Iraq told The Associated Press in Baghdad, insisting on speaking anonymously to discuss military matters. He refused to give further details.

An official with a Lebanese Iran-backed group, also insisting on anonymity, said fighters from Iraq's Popular Mobilization Forces, Afghanistan’s Fatimiyoun, Pakistan Zeinabiyoun and the Iran-backed rebel group in Yemen known as Houthis could come to Lebanon to take part in a war.

Israel is also aware of the possible influx of foreign fighters.

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Eran Etzion, former head of policy planning for the Israeli Ministry of Foreign Affairs, said at a panel discussion hosted by the Washington-based Middle East Institute on Thursday that he sees “a high probability” of a “multi-front war.”

Daniel Hagari, Israel’s military spokesman, said in a televised statement this past week that since Hezbollah started its attacks on Israel on Oct. 8, it has fired more than 5,000 rockets, anti-tank missiles and drones toward Israel.